Influence of Titania Synthesized by Pulsed Laser Ablation on the State of Platinum during Ammonia Oxidation

Round 1

Reviewer 1 Report

Authors present an interesting manuscript on the synthesis, characterization and application of TiO2/Pt catalysts for NH3 oxidation to N2. While the authors performed a very in-depth characterization of the material, some issues must be addressed prior to publication in this journal.

1. A deep characterization is presented. Still, which is the Pt content for each synthesized catalyst? I suggest measurement by ICP. 
2. Please restructure the manuscript. The results section should include only the graphs, where as the discussion section must be more extense. 
3. Discussion on the catalytic activity section can be improved. So far the discussion is merely describing the graphs. Please care to explain why the catalytic activity is modified using different temperatures in the synthesis or why there is a decrease in the catalytic activity in consecutive cycles for the P25 catalyst.  
4. XPS data before reaction (Table 4) and the comparison between before and after reaction (Table 5) seem incongruent. Please revise this data. 
5. Catalyst stability should be tested performing one NH3 oxidation reaction at the optimum temperature for 100 h with both P25 and PLA supports.  
6. 14 figures and 5 tables seem excesive. Please select the most relevant information and place the rest on supporting material.
7. 62 references seems a bit excesive for a research article with this lenght. Furthermore, excesive autocitation must be avoided (9 citations from the first author). 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript deals with the study of two Pt/TiO2 catalysts prepared by using commercially available TiO2-P25 and a TiO2 support produced by a pulsed laser ablation, respectively. In both catalysts the platinum was deposited by incipient wetness impregnation. The catalysts were then calcined at different temperature (400, 600, 800°C) and the structural and morphological features of the materials were deeply investigated by a set of physicochemical methods (e.g. XPS, XAFS, HRTEM…). The results obtained were properly reported and discussed. The catalysts were studied in the ammonia oxidation reaction carrying out further catalytic cycles. PLA-derived catalysts showed and higher stability and selectivity towards N2 than the analogous ones deposited onto P25. The authors well discuss the structure-reactivity relationship of the synthesized materials. The results can be of interest for the scientific community working on catalysts for the ammonia oxidation reaction and more in general on titania-based catalysts. The paper can be accepted for publication after revising the issues reported below:

• I suggest to revise the title considering that the main topic of the paper is the synthesis of the a new TiO2 support by PLA approach. The platinum was deposited by a conventional approach. This aspect do not appear in the present title.
• Considering that for the PLA synthesis water was used as the only solvent, where into the manuscript is reported “liquid” or "solvent” referred to the PLA approach, it must changed in “water”.
• In the comment of Table 4, the authors reported that “[…]. The increase of the calcination temperature leads to the decrease of the total platinum amount observed by XPS. As XPS is a surface sensitive technique, this decrease might be caused by sintering of platinum in accordance with the XRD data”. I completely agree for catalysts calcined at 600°C respect to the analogous ones treated at 400°C. However, for the catalysts calcined at 800°C, where XRD evidenced a huge increase of the Pt particles size, the data reported in the table showed that the Pt/Ti molar ration increase respect to those observed for the catalysts calcined at 600°C. The authors must add some comments on this.
• Moreover from the data reported in Table 4 it is evident that at the surface of the analyzed samples there is a large amount of carbon impurities. The authors must add some explanations about it considering that neither organic precursors or solvents were used for the preparation of the materials.
• Figure 12 shows that the difference in conversion curves among the two Pt/TiO2 catalysts becomes more marked when the catalysts were calcined at 600°C respect to the analogous ones calcined at 400°C. I think this result is very interesting. Can the authors also report the selectivity of the catalysts calcined at 600°C?

 

Typos:

“XDR” line 478 page 16

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The changes introduced have improved the quality of the manuscript.